The present invention relates to a method and to a system for the production of ethanol. It is particularly applicable to the conversion of methanol to ethanol but also relates to the production of ethanol from gases including carbon monoxide and hydrogen. Such gases are produced in the gasification of coal or other carbonaceous material. Where carbon monoxide and hydrogen along with various gasifier products are provided as raw materials, methanol or a methanol derivative such as methyl formate is contemplated as a reactant or as an intermediate within the process and system of the present invention. Therefore, the present process and system in most instances will be described in terms of the conversion of methanol to ethanol.
The catalytic system employed is a homogeneous system with a transition metal carbonyl in organic liquid solution. One previous system of this type employed dicobalt octacarbonyl as catalyst in organic solvent for the reaction of methanol with carbon monoxide and hydrogen gas. Both ethanol and water were produced along with a large variety of by-products including various ethers, esters and higher alcohols as well as other by-products. Attempts to improve the selectivity or activity of the cobalt catalysts by the addition of various ligands or co-catalysts were reported. Ligands such as phosphines, amines, nitriles, pyridines and phenols with co-catalysts including carbonyls of iron, chromium, manganese, rhenium, rhodium, platinum, copper and vanadium have been tested.
In other prior systems, rhodium carbonyl clusters were deposited on various metal oxides such as silica gel and alumina to act as a heterogeneous catalyst for the reaction of carbon monoxide and hydrogen gas to form products such as ethanol, methanol, acetaldehyde and acetate.
The following patents and other publications are illustrative of the general field of the present development.
U.S. Pat. No. 4,133,966, Jan. 9, 1979, discloses a process for reacting methanol with hydrogen and carbon monoxide to produce ethanol and water in the presence of cobalt acetylacetonate, a tertiary organo group V compound and a ruthenium compound.
U.S. Pat. No. 4,152,248 to Feder and Rathke, May 1, 1979, discloses the use of cobalt octacarbonyl and other transition metal carbonyl catalysts in organic solvent for the hydrogenation of a coal liquid.
Wada and Matsuda, JOMC 61, 365-373, 1973 discloses the formation of mononuclear hydride anion, HFe(CO).sub.4.sup.-, in the reaction of Fe(CO).sub.5 with water or hydrogen in the presence of tertiary amine under carbon monoxide pressure and presents insight into the behavior of iron carbonyl species under conditions comparable to those used in the hydroxymethylation of olefins.
CHEM. ECON. ENG. REV. 11 (5) 15 (1979) "Ethanol from Synthetic Gas" and J.C.S. CHEM. COMM. 1978 "Catalytic Synthesis of Ethanol from CO and H.sub.2 Under Atmospheric Pressure Over Pyrolysed Rhodium Carbonyl Clusters on TiO.sub.2, ZrO.sub.2 and La.sub.2 O.sub.3 " 566-567 disclose the production of ethanol from CO and H.sub.2 gases over pyrolysed Rh carbonyl clusters dispersed on metal oxides.
IND. ENG. CHEM. PROD. RES. DEV. Vol 17, No. 3 1978 Page 231-236 discloses the conversion of methanol to ethanol in organic solution with a cobalt carbonyl catalyst. Water and various other organic compounds are also produced.
C&EN, Apr. 7, 1980 "Methanol Carbonylation Selectivity Improved" 37-38 discloses the conversion of methanol to ethanol over transition metal carbonyl catalysts to produce ethanol and water.
GER. OFFEN. No. 2,625,627 discloses the reaction of methanol with carbon monoxide and hydrogen in the presence of CoI.sub.2 or CoBr.sub.2 a tertiary phosphine and a hydrocarbon to produce ethanol and water.
Ital. No. 484,182, Aug. 29, 1953 presents production of linear primary alcohol mixtures by the reaction of methanol, carbon monoxide and hydrogen in the presence of a catalyst material containing melted iron.
For convenience in describing the present invention, the following abbreviations or symbols will be used:
Me--Methyl group, CH.sub.3 -- PA1 Et--Ethyl group, C.sub.2 H.sub.5 -- PA1 NR.sub.3 --Any tertiary amine with all three positions of the amine nitrogen substituted. Two of the substitutions may be to the same group as in a heterocyclic ring or by a double bond. PA1 TM--Transition metal. PA1 pKa--The negative logarithm of the acid dissociation constant for the acid, HB in water where B.sup.- is the conjugate base, i.e. ##EQU1## Since the catalytic system of this application is in organic solution rather than water, pKa is used as an estimate of relative acidity or basicity. PA1 pH--For purposes of this application, pH refers to actual measurements in organic solutions with commercially available pH meters rather than to the negative logarithm of the hydronium ion concentration which may not be present in the solution.